1. Field of the Invention
The polyester imides of general formula I in which A is a quadrivalent aromatic group with 6-32 C atoms, in which up to 40% of A may be replaced by a quadrivalent aliphatic group with up to 16 C atoms, B is a divalent aliphatic or aromatic group with up to 14 C atoms, Z is an alkylene group with 2-3 C atoms, and n is a number from 3-500, are of high industrial interest due to their high thermal stability and the favorable combination of polyester and polyester imide properties. ##STR3## However, an attractive method for preparing polymers of this class has been lacking. Accordingly, the applications of polyester imides of formula I have been limited to small scale research quantities.
2. Discussion of the Background
In Jap. Pat. App. OS No. 84/120,632, a three-stage method for preparing polyester imides of formula VIII is described. ##STR4## According to this method, a tetracarboxylic acid dianhydride of formula II is first reacted with an ##STR5## amino alcohol of formula IV, to produce the corresponding diamidedicarboxylic acid (V). ##STR6##
This is then condensed with dicarboxylic acid dichlorides (VI) to produce polyamide carboxylic acid esters of general formula VII, and in a third step the polyamide esters are dehydrated to form polyester imides of formula VIII. ##STR7##
This method is costly, not only because it requires three steps, but because it uses dicarboxylic acid dichlorides, which are difficult to handle. Furthermore, a number of interfering side reactions are possible, and the only way to suppress these reactions to any substantial degree is to adhere stringently to specific reaction conditions. The acid dichlorides present a particular problem in that the product itself can be damaged by formation of HCI.
It is also known from Ger. OS No. 12 57 778 to produce N-2-acyloxyethylphthalimides of general formula X, where R represents a hydrogen atom, an alkyl group, or a phenyl group, by reacting phthalic anhydride with N-2-hydroxyethylcarboxamides of general formula IX. ##STR8##
It is surprising to one skilled in the art that the primary amide bond in this case is so easily broken, and forms the structure with a secondary amide and an ester adjoining each other. It would not be expected that an amide rearrangement reaction (transamidation) could be carried out so easily on difunctional compounds such as III, because this would require a completely unitary, i.e., one-stage course of reaction. ##STR9##